Charlie Brook said she rushed to the front of her flat after hearing a bang just before 10.30am and saw the pavement "had been blown up". She said: "The first explosion blew paving slabs off the pavement creating a hole."

She began filming to alert authorities when the second explosion happened. "Obviously, I was frightened," Brook said. "You could be someone walking along the pavement and be on the spot when it happened – it's a very busy area."

Fireball explodes from pavement in Pimlico. Photograph: ITN

Her video showed a stunned bystander fleeing as flames shot from the ground. The Health and Safety Executive said it was looking into the explosion. Cables on Pimlico Road carry up to 11,000 volts.

A spokesman for UK Power Networks, which maintains the electricity distribution network in the region, said: "At 10.25am [on Thursday] a fault on our underground electricity network in Pimlico Road interrupted power supplies to 1,867 customers.

"UK Power Networks engineers rerouted supplies to 861 customers within 10 minutes and all supplies were reconnected by 1.55pm. Safety is our top priority and the cause of this incident is being investigated."